In the death of former Japanese prime minister Shinzo Abe, Taiwan has lost a staunch supporter who time and again spoke of the importance of the self-ruled island to peace and stability in the Indo-Pacific region.

Abe was seen as Japan's most pro-Taiwanese leader and his shooting shocked the island, with the public and rival politicians alike condemning the act.

On Friday, the skyscraper Taipei 101 was lit up with messages paying tribute to Abe. Taiwanese President Tsai Ing-wen also ordered government bodies and public schools to fly flags at half-mast on Monday in remembrance of the late leader.

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Abe was shot twice in the back on Friday by a 41-year-old male suspect brandishing a home-made shotgun, according to Japanese media reports.

He had been campaigning on the street in the city of Nara for the Diet's upper house elections scheduled for July 10.

Taiwanese leaders, including Tsai, Premier Su Tseng-chang, and former leader Ma Ying-jeou, condemned the act and offered their condolences to his family.

"I feel pain and deep regret with the unfortunate death of former Japanese prime minister Abe, who had been my friend for more than 10 years and who was also a staunch friend of Taiwan," Tsai said in a Facebook post on Friday.

She lauded Abe for his support for Taiwan over the years, including after a destructive earthquake in Hualien in 2019.

Abe helped to promote Taiwan's pineapple industry in 2021 after Beijing banned imports of the fruit, and urged the Japanese government to donate urgently-needed Covid-19 vaccines to Taiwan last year, Tsai noted.

After stepping down in 2020, Abe was considered a vocal advocate of the island's security in the face of continued military threats from Beijing, which views Taiwan as its own and vows to control, by force if necessary.

According to news agency Kyodo, Abe was the first Japanese leader to suggest that "a Taiwan contingency is a contingency for Japan".

"In other words, it is also a contingency for the Japan-US alliance. People in Beijing, particularly President Xi Jinping, should not misjudge that," he was quoted as saying.

Abe also repeatedly called on the United States to abandon its "strategic ambiguity" on the defence of Taiwan in a cross-strait conflict, saying Beijing would be more cautious about an attack if it had to consider an American reaction.